morphological
differences between male and female animals. The adult males possess
an enlarged claw and a smaller, normal one, while the females have
two equal-sized small ones. Only the small claws, with their spoon-shaped
tips are used for feeding. The larger claw is used for courtship,
warning and fighting.

Two species are especially
common in open sandy/muddy areas. U. annulipes has a black shell
with blue or white stripes and a smooth orange to red claw, while the larger
U. vocans has a greyish-blue body and large, rough orange claws.
The colour of the females tend to vary. Another species occasionally encountered
is the beautiful scarlet red U. rosea from mangroves. (Body up to
3crn in width).